This invention relates to a shutter for a cartridge, such as a magnetic disk cartridge, an optical disk cartridge and a magnetic tape cartridge, and also to an apparatus for molding such a shutter. More particularly, the invention relates to the thickness of a flat plate portion of the shutter and to the construction of the mold for molding this flat plate portion.
FIG. 1 is a perspective view of a magnetic disk cartridge, FIG. 2 is a cross-sectional view taken along the line II--II of FIG. 1, and FIG. 3 is a perspective view of a shutter used in the magnetic disk cartridge.
A flexible magnetic disk 2 is rotatably housed within a cartridge case 1 composed of an upper case member 1a and a lower case member 1b (see FIG. 2) connected together. A pair of recesses 3 are formed respectively in opposite sides of the front portion of the cartridge case 1, and a magnetic head insertion hole 4 is formed in a generally central portion of the recessed portion 3. A shutter 5 for selectively opening and closing the magnetic head insertion hole 4 is slidably supported on the recessed portion 3.
The shutter 5 is made of either metal or a synthetic resin. In the case of the metal shutter 5, the edges of the shutter 5 grind or cut the sliding surface of the recessed portion 3 during the sliding movement of the shutter 5, so that powder of a synthetic resin is produced by such grinding. This synthetic resin powder adheres to the magnetic disk 2, so that an error is liable to occur during the recording and reproduction. In an attempt to prevent this, if a large clearance is provided between the cartridge case 1 and the shutter 5, foreign matter such as dirt is liable to intrude into the cartridge case 1 from the surroundings of the shutter 5. As a result, such foreign matter adheres to the magnetic disk, so that an error is also caused during recording and reproduction.
On the other hand, the synthetic resin shutter 5, unlike the metal shutter, is free from the problem that the surface of the recessed portion 3 is ground. Therefore, the shutter 5 can be disposed in resilient, close contact with the surface of the cartridge case 1, i.e., the recessed portion 3, thereby effectively preventing foreign matter, such as dirt, from intruding into the cartridge case 1 from the surroundings of the shutter 5.
As shown in FIGS. 2 and 3, the synthetic resin shutter 5 is comprised mainly of a pair of opposed flat plate portions 6 and a connecting plate portion 7 interconnecting the two flat plate portions 6 at their one end edges. The synthetic resin shutter 5 has a generally U-shape as viewed from the side thereof. Each flat plate portion 6 has an opening 8 of generally the same size as that of the magnetic head insertion hole 4, and a closure portion 9 for closing the magnetic head insertion hole 4. As shown in FIG. 1, this shutter 5 is normally urged resiliently by a spring (not shown) in such a direction that the closure portion 9 closes the magnetic head insertion hole 4.
Key-shaped projections 10 are formed on the inner surface of the connecting plate portion 7. As shown in FIG. 2, the key-shaped projections 10 are engaged in a guide groove 11 provided inside the cartridge case 1, thereby preventing the shutter 5 from being disengaged from the cartridge case 1 during the sliding movement of the shutter 5. Openings 12 are formed through those portions of the flat plate portions 6 opposed to proximal portions 10a of the projections 10. The openings 12 are formed when releasing a mold.
In the conventional shutter 5, particular consideration has not been given to the thickness of the flat plate portion 6, and the flat plate portion 6 has a uniform thickness as a whole.
On the other hand, in view of the uniformity of flow of the resin, a gate for injection-molding the shutter 5 is usually disposed at a position corresponding to the end edge of the connecting plate portion 7. Therefore, when the shutter 5 is actually injection-molded, the flow of the resin is worse at the free end portion of the flat plate portion 6 remote from the connecting plate portion 7, so that a short shot or a void tends to occur at the free end portion of the flat plate portion 6 whereas the flat plate portion 6 becomes thicker at its proximal end portion close to the gate, so that burrs may be formed on this proximal end portion. Particularly, with respect to the type of cartridge in which the flat plate portion 6 is quite thin, on the order of about 0.35 mm, as in a 3.5-inch magnetic disk cartridge, or with respect to the type of cartridge in which a flat plate portion is so long (in a direction perpendicular to the direction of sliding movement of the shutter), as to close both a head insertion hole and a drive shaft insertion hole as in an optical disk cartridge, the above-mentioned short shot and void tend to develop at the free end portion of the flat plate portion 6. Thus, in the prior art, a defective molding of the shutter 5 has been liable to occur, which affects the productivity.
FIG. 15 is a plan view of a portion of a magnetic disk cartridge employing a conventional shutter 5 of a synthetic resin. As shown in FIG. 15, a notch 13 for opening the shutter 5 is provided at the front face of a cartridge case 1. When the magnetic disk cartridge is inserted into a recording and reproducing device, a distal end of a shutter-opening member 14 provided on the recording and reproducing device is inserted in the notch 13, and is engaged with the side edge of the shutter 5, disposed in its closed position, to urge the shutter 5 to be automatically opened in a direction of the arrow in response to the insertion of the magnetic disk cartridge.
On the other hand, a gate trace 15 is formed at that end of the conventional shutter 5 close to the opening 8, and the gate trace 15 of a tapered shape is projected from the end of the shutter 5. Therefore, the shutter 5 and the shutter opening member 14 fail to positively engage each other, and in some cases the shutter opening member 14 is not engaged with the shutter 5, but slides over the shutter 5. Thus, the problem of operation reliability has been encountered.